High-temperature turbine



Patented Aug. 24, 1948 HIGH-TEWATUBE manner:

I William Charles Clarke, Jr., Dundalk, Md., assignor to Armoo Steel Corporation, a corporation of om No Drawing. Application February 1,1948, Serial N0. 645,015

l 3 Claims.

My invention relates to high-temperature turbines, especially gas turbines, gas turbine parts, and related equipment.

Among the objects of my invention'is the provision of tough, strong and reliable turbine parts, as for example wheels, rotors, blades or buckets, which are suitable for high-temperature duty and oii'er great strength and high resistance to corrosion in actual practical use where high temperature stresses in combination with the wash and scour of hot gases are encountered.

The invention consists in the turbine construction, especially the combination of elements, composition of ingredients and features of construction. employed therein, all as described herein. the scope of the application of which is indicated in the following claims.

As conducive to a clearer understanding of certain features of my invention, it may be noted at this point that gas turbines are subjected to highly damaging high-temperature eii'ects during operation. Many of the turbine parts, for example turbine blades, rotors, wheels, buckets, nozzles, and the like, are even directly exposed to the heating effects of the hot turbine-propelling gas. Under these high-temperature conditions the parts tend to warp, or fail for lack of strength and toughness. These deficiencies impose limitations on the life and efllciency of operation of the turbine.

In addition, under actu'al operating conditions, the interior of the turbine is directly contacted by the hot propelling gas. Direct scouring, and this usually either under oxidizing or reducing conditions, results. The parts consequently are inclined to pit and corrode so extensively as to diminish their effectiveness, or require replacement. The corrosive attack is accelerated by the severe temperature conditions under which certain of the parts function. The vibration encountered in use, as well as the stresses of operation, directly contribute tofailure. In numerous instances the very nature of the metal employed makes the equipment susceptible to em brittlement, creep or fatiguing eflects of high temperature, often coupled with corrosion or the formation of heat scale.

In way of further comment it may be said on the one hand, that the usual well-known carbon steels offer a variety of desirable properties at room temperature, but lose many of their valuable characteristics through exposure to the elevated temperatures encountered in turbinecoperation. A similar observation applies to numerous types of stainless steels. Although many of these alloys fall into the heat-resisting class, they still fall short of meeting the exacting requirements of turbine use. Known heat-resisting alloys of the high-temperature group, on the other hand, are notoriously diflicult to work and therefore the production of wrought turbine equipment'from the same presents no small problem, even on the assumption that the metal possesses the desired properties for eventual use as a finished product.

An outstanding object of my invention accordingly is the provision of turbine parts which are resistant to the wash and scour of turbine-propelling gases at elevated temperatures. and which are heat-resistant. mechanically strong, tough and durable under the peculiar conditions of use.

Referring now more particularly to the practice of my invention. I find that by properly selecting and correlating in a steel the ingredients chromium, nickel, molybdenum and copper with additions of manganese, columbium, and titanium, the carbon content being kept low, to give a fully austenitic steel, satisfactory hot-work properties are had. Such steel readily may be forged into the desired high-temperature turbine parts. Moreover, such parts as, for example, shafts,bolts, rivets, blades, buckets, wheels and rotors, and the like, possess desired operating characteristics. More specifically, I find that turbine parts containing 0.05% to 0.15% carbon. 12% to 22% chromium, 10% to 21% nickel, from 0.10% to 2.0% manganese, 2% to 4% molybdenum, copper ranging from 2% to 4%, from 0.15% to 0.75% titanium, 0.20% to 1.10% columbium. and the remainder substantially all iron possess excellent properties in use.

These parts are wholly austenitic in structure. Ferrite, if present at all, is only in traces. This I find essential to the required high stress-rupture properties. Where appreciable amounts of ferrite are present the stress-rupture values fall 011. Also, as noted above, the working qualities of the metal sufler.

- The composition limits given are considered to be in every sense critical since I find that where they are departed from one or more of the desired qualities suffer. For example, with a higher carbon content the working properties suii'er and the parts are not so easily produced. To like eifect with a manganese content exceeding 2.0% there is a loss in hot-working properties. With any appreciable lowering of the molybdenum and copper contents the desired high-temperature characteristics of the turbine sufler and with appreciable increase workability iii maximum, 17% chromium, 13% nickel, from 1.0% to 1.5% manganese, 3.0% molybdenum, 3.0% copper, 0.25% titanium, 0.40% columbium and the remainder substantially all iron. Inch dental amounts of phosphorus, sulphur and sili con, of course, are present, the latter not enceeding 0.7% and the other two not exceeding 0.03%.

As illustrative of the practice of my invention austenitic chromium-nickel stainless steel first is produced, this for example in the form oi ingots, in the manner described in Patent No.

1,925,182 of Alexander L. Field. These ingots are then re-hoated and fashioned into billets by hot-rolling or forging from a temperature of about 2250 The billets then are forged into roughly formed shaits, bolts, wheels, buckets and the like. Machining to final size is achieved as desired. Fabrication of certain parts by welding with the oxyacetylene torch, or electric are means, employing welding rods preferably of approximately the same analysis as the stock being welded, is undertaken where desired.

As a matter of further preference, subsequent to the rough forging and then machining of my turbine parts. I age the same by heating at a temperature of say 1200 F. for about five hours. These are then air-cooled and piclded.

The turbine equipment which I provide is cor rosion-reslstant and heat-resistant. Moreover, it is capable of withstanding the exacting conditions of duty at temperatures up to about 1500 F. or more. over long periods of continuous use without grain growth, fatigue or failure, In use, the turbine parts display reliable strength in tension, compression and torsion. They are resistant to warping, and resist harmful scaling and attack by oxidizing or reducing gases.

In way of further illustration of properties, a sample of forged and aged metal (forged from 2250* F. and aged at 1200 F. for about five hours followed by air-cooling) taken from my turbine parts and analyzing approximately 0.097% car--v bon, 16.93% chromium, 13.10% nickel, 1.21% manganese, 2.98% copper, 2.95% molybdenum, 0.21% titanium, 0.43% columbium and the remainder substantially all iron, at the end of a 1000 hour tensile test, at 35,000 p. s. i. at 1200' F. had a total extension of 0.60% in a 2-inch gauge length. This represents a rate of elongation of 0.000218% per hour. It therefore can be seen from the present example that the elevated temperature properties of my stainless steel articles and products are of an extremely high order with respect to resistance to elongation and creep.

I have exposed other samples of turbine steel oi the composition noted to stress rupture tests at 1200 F. and found the same to endure a 49,000 pounds per square inch stress for hours, and 43,000 p. s. i. for 100 hours, and 38.500 p. s. i. for 1000 hours.

Still other samples, these analyzing 0.090% carbon, 17.53% chromium, 13.18% nickel, 2.99% molybdenum, 2.99% copper, 0.42% columbium.

7 4 0.29% titanium. 1.21% mainder substantially all iron, were prepared and subjected to test with the following results:

Stress-rupture test at 1200 F.

{Condition A, annealed at 2050 F. for five hours and water quenched] Stress Time P. a. 1. Hours 48, 000 10. 40, 260 84, 600 1,000

[Condition B, annealed at 22 F. or onc-l1all hour and water quenched plus aging at 1200 F. for live hours and water quenched.)

Stress Time P. a. i. Home eaeoo 10 48.000 l00 2 8, 560 1,000

'reep Tests Rate of Extension, per Test. Initial Extcncent in Condition Temper- Loud Extenslon alter 100,000 hrs.

ature slcn 500 hrs. between 900th and 1800i): hr.

F. P. a. I. Per cent Per cent 1, mo 13, 000 .140 1. 1 l, 200 m 000 145 .180 88 1, 350 i0, 000 055 l. 07

virtue of the particular combination of elements therein, both the remarkable ability to be worked during the product manufacturing operations and to withstand conditions surrounding the use of the resulting finished products.

Thus it will be seen that there is provided in this invention austenitlc chromium-nickel alloy gas turbine parts or articles in which the various objects noted, together with many thoroughly practical advantages are successfully achieved. It wil1 be seen that the turbine parts are tough, strong, durable, corrosion-resistant, heat-resistant and are especially adapted to withstand continuous high temperature duty over long periods of time and under the many conditions of actual practical use.

While the invention is particularly concerned with gas turbines and their associated rotors, buckets and the like, I find that high-temperature steam turbines satisfactorily are constructed in accordance with my invention. Satisfactory operation of such turbines is had at temperatures of 1000 F. to 1100 F., or higher.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiment hereinbefore set forth.

it is to be understood that all matter describedv herein is to be interpreted as illustrative and not in a limiting sense.

manganese, and the re 2% manganese, 2% to 4% molybdenum, 2% to 5 4% copper, 0.15% to 0.75% titanium, 0.20% to 1.10% columbium, 0.01% to 0.15% carbon, and remainder iron, characterized by resistance to fatigue and creep and by resistance to attack by corrosive gases under conditions of high temperatures.

2. Wrought turbine parts comprising 17% chromium, 13% nickel, 1% to 1.5% manganese,

3% molybdenum, 3% copper, 0.25% titanium and 0.40% columbium, 0.10% maximum carbon, and 15 remainder iron, said parts being fully austenitic and characterized by resistance to fatigue and creep and by resistance to attack by corrosive gases under conditions of high temperatures.

3. A turbine bucket comprising 12% to 22% chromium, 10% to 21% nickel, 0.10% to 2% manganese, 2% to 4% molybdenum, 2% to 4% copper, 0.15% to 0.75% titanium, 0.20% to 1.10% columbium, 0.01% to 0.15% carbon, and remainder principally iron, characterized by a fully austenitic structure and by resistance to fatigue and creep and by resistance to attack by corrosive gases under conditions of high temperatures. WILLIAM CHARLES CLARKE, Jl.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED sums PATENTS 10 Number Name Date 1,542,232 Girin June 16, 1925 1,736,053 Rohn Nov. 10, 1920 1,800,730 Holzwarth Apr. 14, 1031 1,962,702 Armstrong June 12, 1934 2,115,733 Krivobak May 3, 1980 2,159,724 Franks May 23, 1030 2,251,163 Payson July 20, 1941 2,256,614 Franks Sept. 23, 1941 FOREIGN PATENTS 20 Number Country Date 497,511 Great Britain Dec. 21, 1930 851,496 France Oct. 2, 1039 OTHERREFERENCES "Titanium and Columbium in Plain High- Chromium Steels" in the "magazine The Iron Age.

Oct. 26, 1933, pp. 20-22. 

